Evaluation of Harpin for the Control of Insect-Vectored Bacterial Wilt of Pumpkin and Testing of PMR-Pumpkin and Squash Varieties for Their Reaction to Beetle Feeding Activity and Bacterial Wilt Inoculations 1999
Project Leaders: Margaret Tuttle McGrath, Dept. of Plant Pathology, Riverhead
Thomas A. Zitter, Dept. of Plant Pathology, Ithaca
Michael P. Hoffmann, Dept. of Entomology, Ithaca
Steven V. Beer, Dept. of Plant Pathology, Ithaca
Chuck Bornt, CCE, Orleans Co.
Dan Gilrien, CCE, Suffolk Co.
Maire Ullrich, CCE, Orange Co.
John Mishanec, Eastern NY Vegetable IPM Specialist
Roger Powers, grower, Pittsford, NY
The goals of this project were 1) to determine if harpin can suppress the transmission of bacterial wilt (BW) vectored by cucumber beetles and 2) to compare cucurbit crops and varieties for their attractiveness to cucumber beetles and susceptibility to bacterial wilt. Recently there has been a dramatic increase in the occurrence of BW, especially in pumpkin and squash, and a new disease has appeared that is caused by the same bacterium (Erwinia tracheiphila). Harpin, the active ingredient in Messenger, is a protein originating from Erwinia amylovora. It has been shown to induce the natural defense system of plants (known as Systemic Acquired Resistance or SAR) for several diseases and to reduce insect attractiveness of treated plants. Messenger would be a safer alternative to chemicals that may be restricted or eliminated for cucumber beetle control as a result of The Food Quality Protection Act.
Pumpkins receiving both seed and foliar Messenger treatments had significantly less feeding damage and wilt than nontreated in the experiment conducted in Suffolk County. The difference in damage, however, was small (4.6% vs 5.8%). Incidence of bacterial wilt was significantly lower for plants treated with Messenger than nontreated on 2 of the 4 assessment dates. Incidence was 26-28% for Messenger-treated plants and 48% for nontreated on 21 July. However, disease pressure was very high in this experiment and almost all plants developed wilt by 17 Aug. In sharp contrast, bacterial wilt did not develop in the experiment conducted in Tompkins County or the experiment conducted in a commercial grower’s field in Monroe County. Also there were no significant differences in feeding damage in the Tompkins County experiment. Additional research with higher rates and/or more than 3 applications is warranted.
Substantial differences were detected among cucurbit crops and among varieties in attractiveness to beetles and susceptible to wilt. The gourd Turk's Turban was very attractive to beetles and susceptible to wilt in the Suffolk County experiment. Turk's Turban also had more feeding injury than the gourd Pear Bicolored in the Tompkins County experiment. In contrast, watermelon and the winter squash Waltham Butternut did not develop bacterial wilt. Generally crops and varieties with the highest density of cucumber beetles and the most feeding damage had the highest incidence of bacterial wilt: the gourd Turk's Turban, the winter squashes Golden Delicious and Blue Hubbard, the yellow summer squash Goldbar and the muskmelon Athena. However, while the pumpkins Harvest Moon and Howden had higher beetle infestations than Merlin, they had lower incidence of BW. PMR Merlin was demonstrated to be more susceptible to wilt than other pumpkin varieties: 89% of Merlin plants but only 3% of Harvest Moon plants developed severe wilt by 25 Aug. Fortunately the PMR muskmelon and yellow summer squash varieties evaluated were not more susceptible than other varieties without resistance. A threshold of 1 beetle/plant for insecticide treatment appears to be inadequate for managing bacterial wilt in susceptible crops such as cucumber and susceptible varieties such as Merlin considering the high incidence of wilt that occurred although this threshold was not reached in either cucumber variety examined or in Merlin. While there were similarities in rankings of crops and varieties in amount of feeding damage at the two different locations, there were some differences which indicate the need for additional research.
A survey of commercial fields in New York revealed important information about BW occurrence and symptoms. Substantial losses due to BW were detected in new counties, including Madison, Ontario and Yates. Generally fields that had significant amount of losses in 1998, failed to show much infection in 1999, making predictions difficult. At least four different symptoms and time of occurrence were identified for summer squash and pumpkin.